Electric resistance heater for high temperatures



B. BAUER AND A. VON ZEERLEDER.

ELECTRIC RESISTANCE HEATER FOR HIGH TEMPERATURES.

APPLICATION FILED 050.10, 1919.

1,426,245, Patented Aug. 15, 1922 high temperatures is also known.

however have not been found satisfactory,

u N l Ares PA ENT OFFICE.

B UNO BAUER, or z-u rc'n' ALFRED VON zEERLED R, 0E GENEVA, swITaERLAND,v

AssIeNoRs' To soc SWITZERLAND.

' TE A oNYM 'DEs ATEL ERs DE sEcHERoN, or GENEVA.

EL CT IC REsisT NcE HEATER 170R HIGH TEMPERATURES.

1,426,245, Spdcification of Letters Patent. Patented Aug. 15, 1922Application filed December 10, 1919. Serial No. 343,519.

in Electric Resistance Heaters for High Temperatures, of which thefollowing is a full, clear, and exact specification.

The employment of resistance memes,

which are stable at high temperatures is known for electric laboratoryfurnaces, in using these masses for making electric heaters forindustrial purposes the supply of cur rent is beset with difficulties,which render their use difficult in practice. Then, too, the use ofresistance rods of materials stable at Such rods since they areextremely fragile and, in contact with foreign bodies, are subjected todecomposition, to say nothing of the fact that the supply of the currentis technically unreliable. For these reasons, none of the forms hithertoknown has stood the test of practice.

The present invention relates to an elec trical resistance heater forhigh temperatures; which is extremely suitable for tech nicalemployment.

This resistance heater combines with a jacket like heating body ofmouldable stable resistance material, i. e. of such resista'nce materialthat is not affected at hi h temperatures, current supplying rod-li eelectrodes of a similar or analogous material i. e., not fusing at thetemperatures under notice, up to about 2,000 C., these electrodes beingarranged at both ends of said resistance heating body and extending farenough into the body of the heater to permanently secure a reliablesupply of current to the same. These electrodes may be made of silundum,carborundum, kryptol (that is a mixture of graphite, carborundum andclay) et.c-., or of carbon or graphite rods, which atthe highly heatedpoints assume a protective layer at the expense of the resistance mass.Preferably they project from above and below intothe heating mass toconvey the current along becomes electrically conductive at hightemperatures, so that a shunt can be formed through-the masonry betweenthe current su plying poles. To obviate this, the enve ope :of masonryor refractory material is advantageously provided with one or moretransverse insulating'partitions or screens preventing any electricshunt through-the heated masonry.

To protect the current supply poles against the high temperaturesexisting within the furnace and to thus efficiently save the same, thecurrent supply poles can be arranged near to the outer wall of themasonry of the furnace and, if desired, a layer of heat insulatingmaterial, such as burnt clay powder, quartz-sand, asbestos etc., may beinserted between them and the resistance heating bodyjl on using amouldable resistance heating mass of the kind described, it has beenfound, that its resistance is greater in coldstate than after itsheating. It results therefrom that for the starting of the heating body,higher tensions are required than afterwards, if the full charge shallimmediately be obtained. To lessen this drawback, there can additionallybe inserted into the resistance mass a certain number of thin rods ofsimilar or analogous material to that of the current supply electrodes.These additional rods conveying the current when being in the coldstate, become rapidly heated and then transfer their heat to thesurrounding heating mass, so that the specific resistance therof isdiminished and the current can be turned over to the heating mass. Thecurrent received by said additional rods is only small as compared withthat which is received by the heating body in the hot state.

Figures 1 and 2 of the accompanying drawing show, by vertical section,two forms of the improved resistance heater as being applied to acrucible furnace.

In the first form represented by Figure 1, the entry and exit of thecurrent take place at the poles 2, of metal, carbon, or graphite, whichmay be provided with water cooling means at 3, and carry the crurentsupplying electrodes 1, in the form of rods, arranged in the upper andlower part of the resistance heating body 4 of the heater. vTheelectrodes 1 consist of a similar or analogous resistance materialstable at high temperatures, or infusible, to that whichconstitutes themouldable resistance body 4 that serves for the actual heating, and theyextend sulficiently far into the interior of the heating body 4 tofurnish a' steady passage for current under all circumstances, even ifthe heating mass should sinter. By the use of similar materials or ofmaterials of the same nature for the electrodes and the heating body, achemical action between the two, which might result in theirdecomposition, is avoided. Then too, the electrodes and the heating bodyhave the same co-efiicient of expansion during heating. By usingelectrodes which are stable at high temperatures we obtain a greatsecurity in working as compared with metallic ones.

The heating mass is so formed in the example shown in the drawingclosely fitting heating jacket fora crucible. The resistance heatingbody can very extensively be adapted to the needs of industry. It may beused in the form of a jacket for rotary or mufile furnaces, or as platesor rods for reheating, hardening, or hearth furnaces, or other heatingapparatus. The heater may be constructed for continuous or single-phaseor polyphase current. By suit ably modifying t e cross .section of theheater, the lowest or highest: heat may be applied at fixed zones of theheater. For instance, by enlarging the cross section of the heater atthe current supplying polesinj urious heating of the latter may beavoided, and, similarly, by diminishing the cross section of the heaterat the lower part of the crucible higher heating may be effected.

In order to avoid any current losses through the masonry 5 surroundingthe heating body 4, at the existing high temperatures, the masonry 5 isprovided with electrically insulating transverse partitions or screens6, for example of mica or asbestos, arranged to prevent any electricshunt through the heated masonry. The number of such protective screensmay vary. A single one may suiiice under certain circumstances.

Fig. 2 shows a second form quite similar} to the first one with regardto the arrangement of the resistance heating'body 4 and of the currentsupplying electrodes 1. To diminish heating of the current supply poles2, the latter are located near to the outer wall of the masonry 5constitutin the envelope of the furnace. Whilst t e lower electrodes 1are arranged vertically, that is parallel to each other, the upperelectrodes 1 lie in a horizontal plane and are radially directed toallow the mountin of the upper current supply poles 2 close y to thelateral outer walls of the masonry. Furthermore,:a refractory andinsulating layer 9, for example of burnt clay powder, quartzsand,asbestos and the like, is inserted beas to form a,

The number of such additional resistance rods 10 depends on the size ofthe heating body. They are designed on the starting of the cold furnace,to rapidly heat the resistance body 4 and to thus render it betterelectrically conductive.

What we claim is:

1. In an electric resistance heater for high temperatures, for electricfurnaces, the combination of a mouldable heating body of any resistancematerial stable at high temperatures, current supply poles arranged infront ofthe upper and lower ends of the resistance heating body,rod-like electrodes of similar resistance material to that of theresistance heating body, carried b said current supply oles and arrangeso as to deeply extend from above and below into the resistance; heatingbody, an envelope of refractory material surrounding the latter,substantially as described. I

2. In an electric resistance heater for high temperatures, for electricfurnaces, the combination of a mouldable heating body of any resistancematerial stable at high temperatures, current supplying poles arrangedat the upper and lower ends of the resistance heating body, rod-likeelectrodes of similar resistance material, to that of the heating body,carried by said current supply poles and arranged so as to extend deeplyinto the resistance heating body, an

envelope of refractory material surrounding said resistance heating bodyand a protective insulating partition or screen extending transverselythrough said envelope bet-ween the upper and lower current supplyingpoles to avoid electric shunt through the envelope when being heated,substantially as described.

3. In an electric resistance heater for high temperatures, for electricfurnaces, the combination of a mouldable heating body of any resistancematerial stableat high temperatures, current suppl poles arranged at theupper and lower en s of the resistance heating body, rod-like electrodesof similar resistance material to that of the resistance heating body,carried by said current supply poles and arranged so as to deeply extendinto the resistance heatin body, an envelope of refractory materisurrounding the latter, said current supply poles being located near tothe outer wall of the envelope and an intermediate heat insulating layerbeing inserted between the current supply poles and the resistanceheating body, for the purpose of reducing .heating of the current supplypoles, substantially as described,

4. In an electric resistance heater for high temperatures, for electricfurnaces, the combination of a mouldable heating body of any resistancematerial stable at high temperatures, current supplying rod-likeelectrodes of similar resistance material, ar-

ranged at the upper and lower ends of the, resistance heating body'so asto deeply ex- 7 Witnesses:

tend thereinto' and thin additional rods of similar material to that ofthe electrodes, in-

serted intojthe resistance heating body and arranged for startingpurposes to rapidly ll singed our names this 12th day of November 201919, in the presence of two subscribing witnesses.

DR. BRUNO BAUER. I DR. v. ZEERLEDER ALFRED.-

J. 'H. CHATENoIs, M. Momma.

